Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart via an external connector assembly having lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Cardiac pacemakers, and other implantable medical devices such as cardiac defibrillators, are hermetically packaged to isolate the device from the body environment. Such devices require that electrical signals be passed between the packaged device and its external connectors, without compromising the hermeticity of the package. Depending on the configuration of the implantable device, there may be multiple electrical paths required between the device and its external connectors. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term connector assembly which does not compromise the hermetic package.
Typically, a hermetic housing feedthrough electrically couples the electronic circuits to a connector assembly. The feedthrough assembly extends through the hermetically sealed outer wall of the housing and into the connector assembly so as to couple the electronic circuits within the housing to lead-receiving receptacles within the connector assembly. Each lead has one or more terminals, typically in the form of pin and one or more conductive rings. When inserted into a receptacle of connector assembly, corresponding contacts within the receptacle come into contact with the terminals on the lead so as to couple the lead to the electronic circuits within the implantable device via the feedthrough assembly. Typically, the lead is fixed or secured within the lead receptacle by one or more setscrews or other securing devices within the lead receptacle. Needless to say, it is imperative that good electrical contact be made between the lead and the connector assembly. At the same time, the connector assembly must be capable of releasing the lead from the lead receptacle during a subsequent surgical procedure.
An example of a connector assembly for receiving a lead is provided by U.S. Pat. No. 4,278,093 of Lafortune et al., which patent issued Jul. 14, 1981, and is entitled "Interchangeable Pacemaker Connector For Leads." In the particular connector assembly described in the '093 patent, the turning of a screw forces a flared end of a collet onto an electrode of a lead.
It is known in prior art connector assemblies to make electrical connection to one or more terminals on the lead by various different connector assemblies including a setscrew, a spring or a compliant electrical contact. It is also known to use a prefabricated connector assembly to hold the electrical contacts together with a series of nonconductive spacers which are made from plastic. The resulting connector subassembly is attached to the pacemaker, or other implantable device, by fixturing it over the pacemaker and having epoxy molded around the subassembly. Alternatively, the connector subassembly may be inserted into a pre-molded connector top and bonded to the pacemaker.
In those prior art connector assemblies in which the lead is fixed within the lead receptacle using a setscrew, the setscrew is often threaded into a connector block within the connector assembly. When the screw is advanced, it comes into physical contact with the pin terminal of the lead. The resulting physical connection is often used as the electrical contact as well. However, this can present one or more problems. For example, the lead is sometimes damaged by the force produced when the setscrew is tightened. Such damage must be controlled, inasmuch as the life of the lead is often longer than that of the pacemaker. Additionally, setscrews in prior art connector assemblies have a history of stripping out of the threaded block. Particularly where relatively small setscrews are used, the threads, or the hex flats, may strip. To minimize or eliminate such problems, setscrews of a certain minimum physical size are necessary. The result is often a hump on the side of the connector assembly as the physical size of the pacemaker and its connector assembly are reduced.
A further problem of prior art connector assemblies relates to the frequent desire or necessity that the terminals be insulated from body fluids. The setscrew and the setscrew block must be insulated from bodily fluids. One solution has been use of a silicone seal, called a septum. The septum forms an insulation barrier between the setscrew and bodily fluids. However, the septum must permit a wrench to pass through it so that the screw can be tightened. Frequently, the septum is damaged by the wrench, with loss of the insulation barrier being a possible result.
Accordingly, it would be desirable to provide a connector assembly for securing or fixing a lead within a lead receptacle in a manner which does not damage either the lead or the receptacle and which permits the lead to be easily removed and then reused where desired. Such connector assembly should also seal against the entry of bodily fluids.
It would also be desirable to provide a connector assembly using relatively small and compact parts which do not require enlargement of the connector assembly or the presence of septums or other protrusions therefrom.
It would still further be desirable to provide a connector assembly which includes a pre-fabricated subassembly having spaces and terminal receptacles therein which may be held in place during epoxy casting for providing a connector top design of modular form.